Patent GB-881724-A (GB)
Title: Improvements in or relating to change-speed transmission mechanisms, notably for automotive vehicles
IPC: F16H63/30
Filed: 1958-05-12
Abstract: 881,724. Change-speed control; change-speed gear; friction clutches; slip couplings. REGIE NATIONALE DES USINES RENAULT. May 12, 1958 [May. 20, 1957; July 24, 1957], No. 15210/58. Class 80 (2). A change-speed gear, particularly for motor cars, comprises a speed-responsive main clutch, and a ratchet clutch in the first or lowest gear ratio path, the other ratios being obtained by selective energization of electromagnetic clutches controlled by an electric relay system not permitted to operate for upshifts except when an engine power regulating member, e.g. the accelerator pedal of an engine driving the changespeed gear, is in such a position that the engine power is shut off. The main clutch may be a centrifugally engaged clutch, or an electro magnetically operated clutch engaged by current supplied from an engine-driven generator, or a fluid coupling. Gearing.-In one form, a motor car change-speed gear comprises a driving shaft 1, Fig. 1, carrying friction shoes 2 radially movable by centrifugal force to engage a drum 6 fast with a shaft 7, driving through a pinion 8 meshing a gear 9 and a ratchet clutch 11 to a gear sleeve 13 which can be positively clutched by a selector sleeve 16 to a driven shaft 10. The lowest or first ratio is accordingly obtained. The selector sleeve 16 also controls the engagement of a reverse ratio by means not further described. To obtain the next highest ratio, a solenoid 39 is energized to attract an armature 44, accordingly connecting a clutch member 4 to the shaft 1 and transmitting drive through an overload slip coupling 30 to a shaft 18 fast with a pinion 17 which meshes a gear 12 integral with the gear sleeve 13, the ratchet clutch 11 overrunning. To engage a third ratio, the solenoid 39 is de-energized and a solenoid 28 is energized to attract the armature 44 and engage a clutch member 5, which transmits drive through a gear 20 to a gear 19 fast on the driven shaft 10. The overload slip coupling comprises a friction disc 38 fast with the second ratio clutch member 4 and lying between a plate 30 fast with the shaft 18 and a two-part plate 31, 36 biased to engage the other side. The inner plate section 31 is connected to the shaft 18 through a torque-sensitive device, comprising a ring of balls 32 lying between radial inclined faces on the disc 31 and a washer 33 fast on the shaft. The outer plate section 36 is axially slidable on the inner plate section 31 and is biased to engage the friction disc 38 by a dished spring washer 37. The arrangement is such that, when the car engine drives through the clutch 4 to the shaft 18, the balls 32 and their coacting inclined faces react to press the inner plate 31 firmly against the disc 38, so that full engine torque is transmitted; however, if, during third-second ratio downshifts, the car tends to drive the engine through the second ratio power path, the balls 32 &c. do not engage the inner plate 31 with the friction disc 38, which latter is only lightly engaged by the spring- biased outer plate 36, and the coupling slips to absorb shocks. The dished spring 37 is of sufficient strength to bias the outer plate 36 firmly enough against the disc 38 to transmit normal overrun torque from the car to the engine during engine braking. Control.-Automatic ratio shifts are obtained by operation of an engine load and road wheel speed electromagnetic device (not further described) sequentially energizing second and third ratio electric relays 48, 49, engagement of a selected ratio being obtained only when the accelerator pedal 54 of the car engine is released. On starting the car from rest, increasing speed of rotation of the input shaft 1 engages the centrifugally operated friction clutch 2 or the equivalent main clutch to drive through the gears 8, 9, the ratchet clutch 11, and the forward-reverse selector sleeve 16 to the output shaft 10, as described above. When the car speed has sufficiently increased, the automatic control device energizes the relay 48 which accordingly closes a switch 48<SP>3</SP> to energize wires 55<SP>1</SP>, 57 from a battery 50 connected through a rheostat 52 adjusted by movement of a rod 53 attached to the accelerator pedal 54. The arrangement is such that when the accelerator pedal 54 is released, the rheostat 51 is adjusted to put the maximum resistance between the battery 50 and the wire 55<SP>1</SP>. The rod 53 also controls a switch 58 which is closed only when the accelerator pedal 54 is released. As long as the accelerator pedal 54 is depressed, the switch 58 is maintained open, and no upshift from the first ratio can be obtained. When the accelerator pedal 54 is released, the switch 58 is closed, and a relay 55 is thereby energized to close a switch 55<SP>3</SP>, so that current from the battery 50 is conducted through a closed switch 56<SP>5</SP> to a wire 46 leading through a brush-andslip-ring 25 and another brush-and-slip-ring 42 to the second ratio clutch solenoid 39, which is energized to engage the second ratio. The ratchet clutch 11 then overruns. On further increase in speed, the third ratio relay 49 is energized by the automatic control means to close a switch 49<SP>3</SP> and connect the battery 50 through a closed switch 61 to an open switch 56<SP>4</SP>. A switch 60, similar to the switch 58, is controlled by the rod 53 so as to be closed only when the accelerator pedal is released. As long as the accelerator pedal is depressed, the switch 60 is maintained open and an upshift into third ratio cannot be obtained. On release of the accelerator pedal, the switch 60 is closed to energize a relay 56 which closes a switch 56<SP>4</SP>, connecting the battery 50 to a wire 47, and simultaneously opens the switch 56<SP>5</SP> to deenergize the second ratio clutch 4. The wire 47 leads through a brush 26 to the solenoid 28 of the third ratio clutch 5, which is accordingly engaged. Downshifts are obtained by operation of the automatic control device successively de-energizing the third and second ratio relays 49, 48, irrespective of the position of the accelerator pedal 54. If a downshift to second ratio takes place when the accelerator pedal 54 is fully depressed, so that the rheostat 51 is set to supply the maximum current to the second ratio clutch solenoid 39, the shock of engagement is smoothed by the slip coupling 30 allowing the car to overrun the engine until the engine speed synchronizes with the speed of the second ratio gear shaft 18. Manual opening of the switch 61 allows the second ratio to be obtained and held at any time for engine braking. As a modification, the slip coupling 30 can be replaced by interposing between the brush 42 and the second ratio clutch solenoid 39 a drag-ring switch 63, Fig. 2, comprising a ring 64 mounted on the clutch hub and carrying friction pads 71 engaging the armature 44. The ring 65 has limited rotational movement relative to the clutch hub, and carries a conducting strip 65 which, when the shaft 18 overruns the armature 44, is moved out of contact with brushes 66, 68 so that the electrical circuit therebetween is broken. Accordingly, energization of the solenoid 39 for a downshift to second ratio is prohibited. As soon as the driving shaft 1 and the armature 44 tend to overrun the shaft 18 following disengagement of the third ratio clutch 5, the drag ring 65 is turned to connect the brushes 66, 68, and the solenoid 39 can then be energized to engage the second ratio clutch 4. In another modification, a modified drag-ring switch 94, Fig. 3, is provided and is controlled by engagement of an electromagnetically operated pilot clutch 90. When a third-second ratio downshift is being established, the clutch 5 is first disengaged, and the wire 46 is energized to supply current through the drag-ring switch 94 to the pilot clutch 90. As long as the shaft 18 overruns the speed of the engine shaft, the pilot clutch 90 causes the drag-ring switch 95 to be opened so that current cannot be supplied to the second ratio clutch solenoid 39. As soon as the speed of the car engine exceeds the speed of the second ratio shaft 18, the pilot clutch 90 turns the drag-ring switch to its closed position, and the second ratio clutch solenoid 39 is accordingly energized. In this form, the control circuit is modified by providing a pneumatic dashpot 76 between the accelerator pedaloperated rod 53 and a switch 73<SP>3</SP> connected to a wire controlling a relay 72 which, when energized, opens a switch 72<SP>3</SP> in the line leading to the second ratio clutch solenoid 39. If the accelerator pedal 54 is released gradually for a second-third ratio upshift, leakage in the pneumatic dashpot 76 prevents the switch 73<SP>3</SP> from being operated, and the establishment of third ratio is obtained as described above. If, however, the accelerator pedal 54 is released rapidly to establish a second-third ratio upshift, the pneumatic dashpot 76 closes the switch 73<SP>3</SP> to energize the relay 72, which opens the switch 72<SP>3</SP> and thereby breaks the circuit to the second ratio clutch 4 before the accelerator pedal 54 has reached its fully closed position. Accordingly, the mechanical drive path through the gear is broken, and the jerk to the car occasioned by the rapid release of the accelerator pedal is obviated. In a further modification, Fig. 4 (not shown), the pneumatic dashpot 76 is replaced by a simple pneumatic servomotor operated in dependence of the inlet manifold depression, a leak within the servomotor prohibiting its action save only when the accelerator pedal is released rapidly.